On Christmas Eve, a massive, Chinese-made maritime oil rig, the Scarabeo 9, arrived at Trinidad and Tobago for inspection. The Spanish oil company Repsol YPF, which keeps regional headquarters in Trinidad, ferried it to the Caribbean to perform deep-ocean drilling off Cuba — whose communist government believes as much as 20 billion barrels of crude may lie near the island’s northwest coast. But it wasn’t Cuban authorities who came aboard the Scarabeo 9 to give it the once-over: officials from the U.S. Coast Guard and Interior Department did, even though the rig won’t be operating in U.S. waters.